Mechanical pulping, alone or combined with a gentle chemical treatment, is widely used in the manufacture of pulps. These processes occur at pH in the range 4-9, and the components of the wood undergo relatively small chemical changes. The pulp therefore has a considerable content of triglycerides, esters and waxes from resin.
Residual resin may cause problems during the subsequent use of the pulp. Thus, agglomerated resin may cause paper breakage during paper manufacture or during printing as well as lowering the paper quality. It is known that the hydrophobic part of resin contains considerable amounts of triglycerides and other esters. It would be desirable to hydrolyze these as the hydrolysis products are more easily removed in aqueous systems.
GB 1,189,604 discloses a process for removing resin constituents from wood chips by applying microorganisms to wood chips during storage. However, decomposition of resin by growth of microorganisms is very difficult to control; temperature, residence time, microbial flora etc. may fluctuate, and the microorganisms may secrete cellulase and hemicellulase that decreases fibre strength and yield.
It is the object of the invention to provide a controllable process for reducing the resin content of pulp with minimal changes of existing equipment and process conditions.